1. Technical Field
The present invention relates to a power-saving circuit for a digital video display device, and more particularly to a power-saving circuit for a digital video display device for detecting whether a transmission minimized differential signaling (TMDS) clock signal is input and performing a power-saving mode according to the detection result.
2. Description of the Related Art
In general, an analog video display device employing a cathode ray tube (CRT) and a digital video display device employing a liquid crystal display (LCD) are widely used for a desktop computer and a portable computer, respectively, wherein the digital video display device employs an analog interface mode and a digital interface mode.
The digital video display device of the analog interface mode has an advantage capable of being directly substituted for the existing analog video display device, whereas the digital video display device of the digital interface mode has an advantage capable of being simple and facilitating the impedance match, so that most portable computers employ the digital video display device of the digital interface mode.
With reference to FIG. 1, FIG. 1 illustrates a power saving circuit 100 of a conventional digital video display device. Operation of the digital video display device of a conventional digital interface mode will be schematically described with reference to FIG. 1 as follows.
In general, graphic card built in a computer main body compresses and encodes horizontal/vertical synchronous signals and a digital video signal into a TMDS data signal and outputs the TMDS data signal to the digital video display device together with a TMDS clock signal. A TMDS driving unit 10 of the digital video display device decompresses the TMDS data signal Data received on line 6, along with a clock signal Clock on line 2 and outputs the horizontal/vertical synchronous signals Hsync and Vsync and the digital video signal DE.
A TMDS signal conversion method is a technology of decoding high-speed serial data received at a receiving side as parallel data and then encoded into the high-speed serial data to be transmitted from a transmitting side, which is widely used in the digital video display device.
The horizontal/vertical synchronous signals Hsync/Vsync and the digital video signal DE output from the TMDS driving unit 10 are input into a display driving unit 12, so that the display driving unit 12 drives a gate driver and a source driver. At this time, a controller 14 carries out a power-saving mode in accordance with whether the horizontal/vertical synchronous signals Hsync/Vsync input from the TMDS driving unit 10 exist.
Since a TMDS signal input to the TMDS driving unit 10 from outside the TMDS driving unit 10 is of a high frequency and a small amplitude, it is difficult for the controller 14 to directly recognize whether the TMDS signal is input. In general, the controller 14 receives the horizontal/vertical synchronous signals Hsync/Vsync output from the TMDS driving unit 10 and indirectly determines whether the TMDS signal is input. That is, if the controller 14 does not receive the horizontal/vertical synchronous signals Hsync/Vsync from the TMDS driving unit 10, the controller 14 enables the digital video display device to carry out a power-saving mode and the controller 14 supplies a power saving signal PS to a power supply unit 16. When the controller 14 receives the horizontal/vertical synchronous signals Hsync/Vsync, the controller 14 enables the video display device to return to a normal mode. The power supply unit 16 supplies an appropriate voltage Vcc to the TMDS driving unit 10, the controller 14 and to display driving unit 12. In order for the controller 14 to determine whether the TMDS signal is input through the TMDS driving unit 10, electric power should be supplied all the time to the controller 14 and the TMDS driving unit 14, even in a power-saving mode.
However, since, in the conventional digital video display device, such as illustrated in FIG. 1, the controller 14 and the TMDS driving unit 10 should be supplied with electric power all the time even in a power-saving mode as stated above, there is a problem in that the power consumption is increased when using the standard of the display power management system (DPMS) of the Video Electronics Standard Association (VESA) for video electronic equipment.